Solar energy harvest using photovoltaic effect requires active semiconducting materials to convert light into electricity. Currently, solar cells based on silicon are the dominating technology due to their high conversion efficiency. Recently, solar cells based on organic materials showed interesting features, especially on the potential of low cost in materials and processing. Judging from the recent success in organic light emitting diodes based on a reverse effect of photovoltaic effect, organic solar cells are very promising. Bulk hetero junction (BHJ) made from phase separated blends of semiconducting polymers and fullerides is a popular structure that has been adopted for polymer solar cells. Current solar cells exhibit low power conversion efficiency, about 4%-5%, compared to silicon based solar cells, even after sophisticated device optimizations.
Conjugated polymers have shown some promise in providing a photovoltaic effect. Conjugated polymers are made of alternating single and double carbon-carbon (C—C) or carbon-nitrogen (C—N) bonds. The conjugated polymers have a 6-bond backbone of intersecting sp2 hybrid orbitals. The pz orbitals on the carbon atoms overlap with neighboring pz orbitals to provide π-bonds. The electrons that comprise the i-bonds are delocalized over the whole molecule. These polymers exhibit electronic properties similar to those seen in inorganic semiconductors. The semiconducting properties of the photovoltaic polymers are derived from their delocalized π bonds.
There is a need in the art for polymer solar cells that exhibit increased solar conversion efficiency.